CN115124067A - For H 2 S detected CuO/WO 3 Method for preparing composite material - Google Patents

Abstract

A preparation method of a CuO/WO3 composite material for H2S detection belongs to the technical field of metal semiconductor gas sensors. The invention aims to provide a preparation method of a CuO/WO3 composite material for H2S detection, which adopts a simple hydrothermal method to synthesize the CuO/WO3 composite material and can efficiently and accurately detect H2S gas. The invention combines WO ₃ Adding the hollow sphere powder into a mixed solution of deionized water and absolute ethyl alcohol, uniformly stirring by using a magnetic stirrer to obtain a yellow solution, and then adding Cu (NO) ₃ ) ₂ ·3H ₂ And O, continuously stirring, adding the mixed solution into a polytetrafluoroethylene high-pressure reaction kettle, transferring the mixed solution into an oven for heating to perform hydrothermal reaction, and automatically performing hydrothermal reaction after the reaction is finishedCooling to room temperature, pouring out the supernatant to obtain precipitate B, centrifuging, collecting the precipitate B, and drying in a constant temperature vacuum drying oven to obtain para-H ₂ S gas sensitive CuO/WO ₃ The hollow sphere composite material. The invention has high sensitivity, good short-term reproducibility and long-term stability, and good selectivity.

Description

Preparation method of CuO/WO3 composite material for H2S detection

technical field

The invention belongs to the technical field of metal semiconductor gas sensors.

Background technique

Hydrogen sulfide (H ₂ S) is a colorless, highly toxic, flammable acid gas. At low concentrations, there is a strong smell of rotten eggs. Long-term exposure will damage the human central nervous system. At high concentrations, people will lose their sense of smell and even cause death in a short period of time. In addition, H ₂ S is easily soluble in water to form a highly corrosive acidic solution, which will affect the operation of production equipment and bring serious economic losses. Therefore, rapid, accurate and economical detection of H ₂ S gas is crucial to human health, industrial production and environmental protection.

Among many H ₂ S gas detection technologies, metal oxide semiconductor gas sensors stand out due to their low cost, fast response, and easy portability. The key part lies in the sensitive material. The metal oxide sensitive materials currently used to detect H ₂ S gas include ZnO, WO ₃ , SnO ₂ , In ₂ O ₃ , CuO, NiO and the like. Among them, WO ₃ is a typical n-type semiconductor with a forbidden band width of 2.6eV-2.8eV, and has its own non-stoichiometric properties and high gas-sensing activity. Therefore, it is widely used in the fields of photocatalysis, photo/electrochromic and gas sensors. In the past ten years, pure WO ₃ materials have performed well in the detection of toxic and harmful H ₂ S gas, but WO ₃ with different structures still has some imperfections, such as low response value, high optimal working temperature, and poor selectivity. Therefore, It needs to be modified to improve gas-sensing properties. The SnO ₂ -WO ₃ material synthesized by Hoa et al. has high response and low detection limit for H ₂ S gas detection, which is mainly due to the formation of nn-type heterojunction between SnO ₂ and WO ₃ (Hoa, TTN; Le, DTT; Van Toan, N.; Van Duy, N.; Hung, CM; Van Hieu, N.; Hoa, ND,Highly selective H ₂ S gas sensor based on WO ₃ -coated SnO ₂ nanowires. Materials Today Communications 2021, 26 , 102094.). Xiao et al. reported a WO ₃ /NiO material with a porous face-centered cubic structure, which can increase the specific surface area and porosity of the material. In addition, the WO ₃ /NiO material generates WS ₂ and NiS intermediates during the reaction with H ₂ S at a working temperature of 250 °C, and the gas sensing performance is significantly improved (Xiao, X.; Zhou, X.; Ma, J.; Zhu , Y.; Cheng, X.; Luo, W.; Deng, Y., Rational Synthesis and GasSensing Performance of Ordered Mesoporous Semiconducting WO ₃ /NiO Composites. ACS applied materials & interfaces 2019, 11 (29), 26268-26276. ). Therefore, in recent years, many research work has mainly focused on improving the morphology and structure of materials and constructing heterojunctions.

Through the investigation of research status at home and abroad, it can be found that WO ₃ has made great progress as a sensitive material for H ₂ S gas sensor, but there are still high production costs, high working temperature, poor short-term reproducibility and long-term stability, and poor selectivity. and other shortcomings, it cannot meet the current practical needs, which limits its large-scale production and application.

SUMMARY OF THE INVENTION

The purpose of the present invention is to use a simple hydrothermal method to synthesize CuO/WO3 composite material, and to prepare a CuO/WO3 composite material for H2S detection which can efficiently and accurately detect H2S gas.

The steps of the present invention are:

(1) Weigh 0.15-0.25 g of WO ₃ hollow sphere powder into a mixed solution of deionized water and absolute ethanol, stir evenly with a magnetic stirrer, and obtain a yellow solution; the volume ratio of deionized water and absolute ethanol is 1:1, magnetic stirring for 25-35 min;

(2) Then add 0.03-0.04 g Cu(NO ₃ ) ₂ ·3H ₂ O to the yellow solution, continue stirring to make the solution evenly mixed; the stirring time is 50-70 min, and the molar ratio of W to Cu is 6:1 ;

(3) The mixed solution was added to a 50 mL polytetrafluoroethylene autoclave, and transferred to an oven for heating for hydrothermal reaction; the oven temperature was set to 170-190 °C, and the reaction time was 4-6 h;

(4) After the reaction was completed, it was naturally cooled to room temperature, and the supernatant was poured out to obtain a precipitate B, which was collected by centrifugation, and washed several times with deionized water and absolute ethanol, respectively, until the supernatant was clear and transparent. The centrifugal speed is 2000-4000 r/min, and the centrifugal washing is performed 6-7 times, the first 3-4 times are washed with deionized water, and the last 3-4 times are washed with absolute ethanol;

(5) Put the obtained precipitate B into a constant temperature vacuum drying oven to dry for 8-12 h to obtain a CuO/WO ₃ hollow sphere composite material sensitive to H ₂ S gas; the temperature of the constant temperature vacuum drying oven is generally set to 60- 70 ℃, the vacuum degree is kept at 700-800 Pa, the heating rate of muffle furnace calcination is 2 ℃/min, and the calcination time is 50-70 min at 490-510 ℃.

The structural form of the CuO/WO ₃ hollow sphere composite material of the present invention is: the form of the CuO/WO ₃ hollow sphere, that is, the morphology and structure of the CuO composite WO ₃ , the diameter of the hollow sphere is 1.2-1.4 μm, and the CuO formed by the copper source is supported in the The surface of the WO ₃ sphere is rough, loose and porous.

The preparation method of the CuO/WO ₃ gas sensor gas sensor material of the present invention: the CuO/WO ₃ hollow sphere material is coated on the surface of the ceramic tube to make a gas sensor element, and the gas sensor element is composed of a ceramic tube, a platinum wire, and a gold electrode , heating wire and sensitive layer; first mix a small amount of synthetic material with deionized water to form a slurry, then dip the slurry with a brush and evenly coat the surface of the cleaned ceramic tube, air dry at room temperature for 30 minutes, insert The nickel-chromium alloy heater was aged for 3 days to enhance its stability, and the prepared gas sensor was put into the gas chamber for the gas sensor performance test.

The CuO/WO ₃ gas sensor prepared by using the CuO/WO ₃ hollow sphere composite material as the main material of the present invention has improved performance in detecting H ₂ S gas response value, and can detect 0.1 to 50 ppm H ₂ S gas in a continuous cycle.

The invention has high sensitivity, good short-term reproducibility and long-term stability, good selectivity, and has the following advantages and beneficial effects:

1. The hierarchically structured hollow sphere _CuO /WO sensor is prepared by a simple two-step hydrothermal method, which does not require any surfactant or template, has low fabrication cost, and is simple to operate, enabling large-scale production and practical application.

2. The response of CuO/WO ₃ composite to 10 ppm H ₂ S is 1297, which is nearly 103 times higher than that of WO ₃ . It is 56.3% higher than the best 10 ppm response reported for this material in the literature to date (830).

3. Due to the sulfidation of CuO and the existence of pn heterojunction, the detection of H ₂ S gas has a high response signal at low temperature (70 °C).

4. The CuO/WO ₃ sensor can perform continuous cycle gas detection for H ₂ S from 0.1 to 50 ppm, with good short-term reproducibility and long-term stability, and the detection limit is as low as 100 ppb.

Description of drawings

Fig. 1 is the XRD spectrum of CuO/WO ₃ material and WO ₃ material prepared by the present invention;

Fig. 2 is the SEM spectrum of CuO/WO ₃ material and WO ₃ material prepared by the present invention;

Fig. 3 is the TEM spectrum of CuO/WO ₃ material prepared by the present invention;

Fig. 4 is a graph showing the relationship between CuO/WO ₃ material and WO ₃ material gas sensor prepared by the present invention to 10 ppm H ₂ S and the optimal working temperature;

Fig. 5 is the response recovery curve diagram of CuO/WO ₃ material and WO ₃ material prepared by the present invention to 10 ppm H ₂ S gas;

Figure 6a shows the dynamic sensing characteristics of CuO/WO ₃ material sensor prepared by the present invention for 1-50-1 ppmH ₂ S at 70°C;

Figure 6b is the response value of the CuO/WO ₃ material sensor prepared by the present invention to 1-50 ppm H ₂ S gas at 70 °C

Figure 6c is the response curve of the CuO/WO ₃ material sensor prepared by the present invention to 5-0.1 ppm H ₂ S at 70 °C (the inset is the original data);

Fig. 7 is the selectivity test chart for different gases prepared by the present invention for CuO/WO ₃ material and WO ₃ material;

Fig. 8a is a graph showing the sensitivity curve of the CuO/WO ₃ material sensor prepared by the present invention exposed to 10 ppm H ₂ S at 70° C. and performing 10 response/desorption experiments on the 10th day;

Fig. 8b is a graph showing the sensitivity curve obtained by the CuO/WO ₃ material sensor prepared by the present invention exposed to 10 ppm H ₂ S at 70°C and 14 times of response/desorption experiments on the 26th day;

Figure 8c is the long-term stability (70°C) test curve of the CuO/WO ₃ material and the WO ₃ material sensor prepared by the present invention to 10 ppm H ₂ S.

Detailed ways

In the present invention, the precursor is synthesized by a hydrothermal method and then calcined to obtain a WO ₃ material, and then a copper source is introduced to synthesize a CuO nanoparticle composite WO ₃ hollow microsphere material. Compared with pure WO ₃ , the gas sensing performance of the CuO/WO ₃ sensor has been significantly improved. At the optimal operating temperature of 70 °C, the response value to 10 ppm H ₂ S is as high as 1297, which is about the same as that of pure WO ₃ . 103 times. In addition, the CuO/WO ₃ sensor can perform continuous cycle gas detection for 0.1-50 ppm H ₂ S with good reproducibility. _The preparation process of the invention is simple, low in cost, does not add any surfactant and template agent, and conforms to the development concept of green chemistry. The field of gas sensors has great production and application prospects.

The improved detection of H ₂ S gas by the CuO/WO ₃ composite material sensor prepared by the invention is mainly summarized in the following three aspects: First, the CuO nanoparticles are dispersed and grown on the surface of the WO ₃ hollow sphere, which not only prevents the aggregation of the CuO particles but also makes the material The surface is rougher. This structure increases the specific surface area and effective adsorption sites, and also provides more transport channels for gas diffusion. Second, _CuO and WO have different Fermi levels, and when interacting, form pn heterostructures and specific electron donor-acceptor systems. Electrons are transferred between the two metals, band bending, accelerating electron transport and thickening the depletion layer. Finally, CuO reacts preferentially with H ₂ S gas to form CuS with metallic properties, the pn junction is destroyed, and the electrical conductivity is significantly improved. Studies have shown that it has excellent gas sensing properties with low operating temperature, good selectivity and high sensitivity.

The present invention is described in further detail below:

1. The preparation method is simple (hydrothermal method),

(1) Add 0.3-0.5 g of WCl ₆ to 30-40 mL of glacial acetic acid, stir with a magnetic stirrer, and the solution changes from dark brown to blue;

(2) Pour the mixed solution into a 50 mL autoclave lined with polytetrafluoroethylene, and put it into an oven for hydrothermal reaction;

(3) After the reaction is completed, it is naturally cooled to room temperature, the supernatant is poured out, the precipitate A is collected by centrifugation, and washed several times with deionized water and absolute ethanol respectively, until the supernatant is clear and transparent;

(4) Put the obtained precipitate A into a constant temperature vacuum drying oven to dry for 8-12 h, and then calcinate in a muffle furnace to obtain a WO ₃ hollow sphere powder sensitive to H ₂ S gas, which is used as a control group ;

(5) Weigh 0.15-0.25 g of the WO ₃ obtained in step (4) into a mixed solution of deionized water and absolute ethanol, stir evenly with a magnetic stirrer, and obtain a yellow solution;

(6) Then add 0.03-0.04 g Cu(NO ₃ ) ₂ ·3H ₂ O to the yellow solution, and continue to stir to make the solution evenly mixed;

(7) The mixed solution was added to a 50 mL polytetrafluoroethylene autoclave, and transferred to an oven for heating for hydrothermal reaction;

(8) After the reaction is completed, it is naturally cooled to room temperature, the supernatant is poured out, the precipitate B is collected by centrifugation, and washed several times with deionized water and absolute ethanol respectively, until the supernatant is clear and transparent;

(9) Put the obtained precipitate B into a constant temperature vacuum drying oven to dry for 8-12 h to obtain a CuO/WO ₃ hollow sphere composite material sensitive to H ₂ S gas, which is used as the experimental group;

The magnetic stirring time in step (1) of the present invention is 25-35 min.

In step (2) of the present invention, the oven temperature is set to 170-190° C., and the reaction time is 11-13 h.

In step (3) of the present invention, the centrifugal speed is 2000-4000 r/min, the centrifugal washing is performed 6-7 times, the first 3-4 times are washed with deionized water, and the last 3-4 times are washed with absolute ethanol.

In step (4) of the present invention, the temperature of the constant temperature vacuum drying oven is generally set to 60-70 °C, the vacuum degree can be maintained at 700-800 Pa, the heating rate of the muffle furnace calcination is 2 °C/min, and the temperature is 490-510 °C. The lower calcination time is 50-70min.

The volume ratio of deionized water and absolute ethanol in step (5) of the present invention is 1:1, and magnetic stirring is performed for 25-35 min.

In the step (6) of the present invention, the stirring time is 50-70 min, and the molar ratio of W to Cu is 6:1.

In step (7) of the present invention, the oven temperature is set to 170-190° C., and the reaction time is 4-6 h.

In step (8) of the present invention, the centrifugal speed is 2000-4000 r/min, the centrifugal washing is performed 6-7 times, the first 3-4 times are washed with deionized water, and the last 3-4 times are washed with absolute ethanol.

In step (9) of the present invention, the temperature of the constant temperature vacuum drying oven is generally set to 60-70°C, and the vacuum degree can be maintained at 700-800 Pa.

2. Vacuum microspheres:

The material was scanned with an x-ray powder diffractometer (XRD-7000, MAXimaCo. Ltd., Japan) to analyze its crystal structure with a scanning speed of 8° min ^-1 and a scanning range of 10°-80°. The morphology and structure of the samples were characterized by electric field emission scanning electron microscopy (SEM, FEI Inspect F50) and transmission electron microscopy (TEM, FEI Tecnai G2 F20).

The gas sensing process of metal oxides is usually carried out on their surfaces. Therefore, the surface topography structure of the material is closely related to the performance of the sensor. Figure 1 shows the XRD pattern of the CuO/WO ₃ hollow microspheres prepared in this experimental case. It can be seen from the figure that these diffraction peaks with similar characteristics are consistent with the standard pattern of monoclinic WO ₃ (JCPDS No.72-0677). , which proves that the synthesized samples are of high purity. The diffraction peaks are located at 23.109°, 23.579°, 24.349°, 33.252°, 34.151°, 49.893° and 55.894°, corresponding to (002), (020), (200), (022), (202) of monoclinic WO ₃ , respectively ), (400) and (420) planes. In addition, the diffraction peaks _of the _CuO /WO3 samples are almost indistinguishable from those of pure WO3, indicating that the crystallinity of the samples did not change, which may be due to the high dispersion of _CuO nanoparticles with small grain size on the surface of WO3. But a closer look reveals that the intensity of the peak increases around 35.50°, which is due to the diffraction peaks at 35.465° and 35.565° corresponding to the (002) and (-111) crystal planes of monoclinic CuO (JCPDS No. 80-1268).

From the SEM images of WO ₃ at different magnifications in part a in Figure 2, it can be seen that WO ₃ presents a hollow spherical shape with a diameter of 0.9-1.1 μm, no other morphology, and the surface of the sample is rough. At the same time, it can be clearly seen that WO ₃ is a three-dimensional spherical structure self-assembled by many one-dimensional nanoparticles. Part b in Figure 2 shows the morphology and structure of CuO composite WO _3. The diameter of the hollow sphere is 1.2-1.4 μm, and the sphere becomes larger. This is because the CuO formed after the introduction of the copper source is loaded on the surface of the WO ₃ sphere, but still remains The original WO ₃ hollow sphere structure was obtained, and the surface became rough. In addition, the surface of the hollow spheres of sample CuO/WO ₃ is more loose and porous than that of WO ₃ , which is due to the solvothermal reaction at high temperature and drying at low temperature, which promotes the formation of pores. The formation of pores is mainly caused by stress release and structural mismatch. On the one hand, the solvothermally prepared CuO/WO ₃ precursor releases stress by forming pores during the high temperature and high pressure reaction to prevent structural damage during crystal growth; on the other hand, the CuO/WO ₃ precursor and hydrate lose The coordination promotes the formation of pores. This special surface structure increases the surface defects of the hollow microspheres and provides more oxygen vacancies and adsorption sites for the test gas.

Parts a and b in Figure 3 show the TEM analysis results of the _CuO /WO3 hollow microspheres. By comparing the bright field and dark field of the atlas, the existence of the hollow sphere structure can be clearly observed, which can provide a channel for gas transport and also a kinetic factor to improve gas diffusion, which is beneficial to the gas sensing performance of CuO/WO ₃ . improve. In addition, the presence of CuO nanoparticles and the coexistence of multiple lattices can be seen from the gray marked points in the figure, which are the result of the coexistence of _CuO and WO3 and the successful construction of the pn heterojunction.

3. The performance of detecting H ₂ S gas response value is improved, and it can continuously detect 0.1 to 50 ppm H ₂ S gas in a continuous cycle

Taking WO ₃ as the control group and CuO/WO ₃ as the experimental group, the gas sensing performance testing and analysis of H ₂ S were carried out.

The working temperature has a great influence on the contact reaction between the gas and the sensitive material, which is closely related to the gas-sensitive characteristic of the sensor. Figure 4 shows the sensor response to 10 ppm H ₂ S gas versus operating temperature. During the gas sensing test, the response curve of the sensor showed the same "increase-max-decay" trend. The sensor exhibits the maximum response at 70 °C, which may be due to the efficient adsorption of H ₂ S molecules and the highest chemical reactivity of the sensing layer at the optimal temperature. Therefore, in the following tests, 70°C was chosen as the optimal working temperature. The response values (Ra/Rg) of WO ₃ and CuO/WO ₃ sensors to 10 ppm H ₂ S are 12.50 and 1297, respectively. It can be seen that the response value of the WO ₃ hollow microsphere sensor modified on the surface of CuO nanoparticles has been significantly improved. About 103 times that of pure WO ₃ sensor.

The response/recovery ability plays an important role in characterizing the gas-sensing properties of materials. Parts a and b of Fig. 5 are the response-desorption curves of WO ₃ sensor and CuO/WO ₃ sensor at 70 °C to 10 ppm H ₂ S. The _CuO /WO composites significantly improved the response time, shortening from 48 s to 13 s (as shown in Table 1), which may be due to the fact that H ₂ S gas would preferentially react with the surface-loaded CuO nanoparticles to form CuS intermediates, which promoted the Fast response of the sensor. After the reaction, it is transferred from the target gas to air. Due to the weak desorption ability and long natural recovery time at low operating temperature, it is necessary to provide a short-time pulse current outside the sensor to accelerate the separation of H ₂ S molecules from the surface of CuO. . WO ₃ and CuO/WO ₃ were heated at 200 °C and 120 °C for 76 s, respectively.

Figure 6a shows the dynamic response curves of the CuO/WO ₃ sensor at 70 °C to different concentrations of H ₂ S gas. The entire testing process is carried out in continuous changes of H ₂ S gas concentration from 1 ppm to 50 ppm to 1 ppm. When exposed to different concentrations of H ₂ S gas, the CuO/WO ₃ sensors all responded rapidly and significantly, and the magnitude of the response increased with the increase of gas concentration. In addition, in the cyclic dynamic test, the CuO/WO ₃ sensor has almost the same corresponding concentration response values in different concentrations of H ₂ S gas, indicating good reproducibility. Figure 6b shows the CuO/WO ₃ material prepared by the present invention. Response of the sensor to _1-50 ppm H2S gas at 70°C. Figure 6c shows the response curves of CuO/WO ₃ at 70 °C to H ₂ S concentrations of 0.1–5 ppm, with a minimum detection limit of 100 ppb of H ₂ S and a response value of 2.34. .

Selectivity is another key metric for gas sensors. In the WO ₃ and CuO/WO ₃ selectivity experiments, the sensors were exposed to 10 ppm of H ₂ S gas, 100 ppm of SO ₂ , NO ₂ , CO and 1000 ppm of ethanol, methanol, ethylene glycol, acetone, respectively, as shown in Figure 7. The results show that the response value of WO ₃ and CuO/WO ₃ sensors to H ₂ S gas is significantly higher than that of other gases at the optimum operating temperature. Compared with WO ₃ , the CuO/WO ₃ sensor has a higher response to H ₂ S gas under the same conditions. This result indicates that CuO/WO ₃ is very suitable for H ₂ S gas detection at low temperature (70℃). Improving the selectivity of CuO/WO ₃ sensor in H ₂ S detection is of great significance for practical applications.

Short-term reproducibility and long-term stability are critical for practical application of MOS sensors. We tested the short-term reproducibility of the CuO/WO ₃ sensor (Fig. 8a, 8b) and the long-term stability of the WO ₃ and CuO/WO ₃ sensors (Fig. 8c) gas-sensing response curves. Figures 8a and 8b show the sensitivity curves of the CuO/WO ₃ sensor exposed to 10 ppm H ₂ S at the optimal operating temperature, and 10 and 14 response/desorption experiments were performed on the 10th and 26th days, respectively. It can be clearly seen that the sensor exhibits good response/desorption performance at the optimal operating temperature with good reproducibility. In the long-term stability test of the CuO/WO ₃ sensor, the CuO/WO ₃ sensor has a negligible drop in the response value within 30 days, and the overall curve remains basically stable with good long-term stability. The negligible degradation of the response may be due to the decrease of CuO/WO ₃ surface active sites and the inability of H ₂ S gas to completely desorb from the material surface, partially forming CuS and other species. Nevertheless, the response value of the CuO/WO ₃ sensor is still much higher than that of the pure WO ₃ sensor.

Table _1. Detection of H2S gas by WO3 _- based materials

。

.

In the design, synthesis and testing of the CuO/WO ₃ sensor in the present invention, graded hollow spherical WO ₃ and CuO/WO ₃ composite materials are synthesized respectively by the hydrothermal method, and are used to detect H ₂ S gas. Using this method, _CuO NPs were synthesized dispersedly grown on the surface of WO3, introducing a large number of reactive sites, and successfully constructed a pn heterojunction. When exposed to 10 ppm of H ₂ S, it exhibits an ultra-high response value of 1297 (Ra/Rg) and an ultra-fast response speed of 13 s at a low temperature of 70 °C. In addition, the selectivity, reproducibility and long-term stability of CuO/WO ₃ (1:6) all performed well. Therefore, the hollow sphere WO ₃ sensor decorated with CuO nanoparticles provides a strategy for realizing low-temperature and high-efficiency detection of H ₂ S gas, with great potential for practical applications.

The specific method for preparing the _CuO /WO gas sensor of the present invention is as follows:

The gas sensor element is composed of ceramic tube, platinum wire, gold electrode, heating wire and sensitive layer. Firstly, a small amount of synthetic material is mixed with deionized water to form a slurry, and then the slurry is dipped with a brush and evenly coated on the surface of the cleaned ceramic tube. After air-drying at room temperature for 30 minutes, it was inserted into a Nichrome heater for aging (3 days) to enhance its stability. Put the prepared gas sensor into the gas chamber for gas sensor performance test.

The preparation method of a CuO/WO ₃ gas sensor gas sensor material for detecting H ₂ S gas is characterized in that, the CuO/WO ₃ hollow sphere material is coated on the surface of a ceramic tube to make a gas sensor element, which specifically includes:

The gas sensor element is composed of ceramic tube, platinum wire, gold electrode, heating wire and sensitive layer. Firstly, a small amount of synthetic material is mixed with deionized water to form a slurry, and then the slurry is dipped with a brush and evenly coated on the surface of the cleaned ceramic tube. After air-drying at room temperature for 30 minutes, it was inserted into a Nichrome heater for aging (3 days) to enhance its stability. Put the prepared gas sensor into the gas chamber for gas sensor performance test.

Example 1

(1) Add 0.3 g of WCl ₆ to 30 mL of glacial acetic acid, stir with a magnetic stirrer for 30 min, and the solution changes from dark brown to blue;

(2) Pour the mixed solution into a 50 mL autoclave lined with polytetrafluoroethylene, and put it into an oven for hydrothermal reaction, the reaction temperature is 170 °C, and the reaction time is 12 h;

(3) After the reaction was completed, it was naturally cooled to room temperature, and the supernatant was poured out. The precipitate A was collected by centrifugation, and washed with deionized water for 3 times and anhydrous ethanol for 3 times, until the supernatant was centrifuged. clear and transparent;

(4) The obtained precipitate A was dried in a constant temperature vacuum drying oven at 60 °C for 8 h, and then calcined in a muffle furnace. With air as the background gas, the temperature was raised to 490 °C at a heating rate of 2 °C/min. , the calcination time is 1 h, and the WO ₃ hollow sphere powder sensitive to H ₂ S gas is obtained;

(5) Weigh 0.15 g of WO ₃ obtained in step (4) into 30 mL of a mixed solution of deionized water and absolute ethanol (volume ratio is 1:1), and stir with a magnetic stirrer for 30 min to obtain a yellow solution ;

(6) Then add 0.03 g Cu(NO ₃ ) ₂ ·3H ₂ O to the yellow solution, and continue stirring for 1 h to make the solution evenly mixed;

(7) The mixed solution was added to a 50 mL polytetrafluoroethylene autoclave, and transferred to an oven for heating for redox reaction at a reaction temperature of 170 °C and a reaction time of 5 h;

(8) After the reaction was completed, it was naturally cooled to room temperature, and the supernatant was poured out. The precipitate B was collected by centrifugation, and washed with deionized water for 3 times and anhydrous ethanol for 3 times, until the supernatant appeared. clear and transparent;

(9) The obtained precipitate B was dried in a constant temperature vacuum drying oven at 60 °C for 8 h to obtain a CuO/WO ₃ hollow sphere composite material sensitive to H ₂ S gas;

(10) Mix 0.03 g of synthetic material with deionized water to form a slurry, then dip the slurry with a brush and evenly coat the surface of the cleaned ceramic tube. After air-drying at room temperature for 30 minutes, it was inserted into a Nichrome heater for aging (3 days) to enhance its stability. Put the prepared gas sensor into the gas chamber for gas sensor performance test.

Example 2

(1) Add 0.5 g of WCl ₆ to 40 mL of glacial acetic acid, stir with a magnetic stirrer for 30 min, and the solution changes from dark brown to blue;

(2) Pour the mixed solution into a 50 mL autoclave lined with polytetrafluoroethylene, and put it into an oven for hydrothermal reaction, the reaction temperature is 190 °C, and the reaction time is 12 h;

(3) After the reaction was completed, it was naturally cooled to room temperature, and the supernatant was poured out. The precipitate A was collected by centrifugation, and washed 4 times with deionized water and 3 times with anhydrous ethanol, until the supernatant was centrifuged. clear and transparent;

(4) The obtained precipitate A was dried in a constant temperature vacuum drying oven at 60 °C for 10 h, and then calcined in a muffle furnace. With air as the background gas, the temperature was raised to 510 °C at a heating rate of 2 °C/min. , the calcination time is 1 h, and the WO ₃ hollow sphere powder sensitive to H ₂ S gas is obtained;

(5) Weigh 0.25 g of WO ₃ obtained in step (4) into 30 mL of a mixed solution of deionized water and absolute ethanol (volume ratio is 1:1), and stir with a magnetic stirrer for 30 min to obtain a yellow solution ;

(6) Then add 0.04 g Cu(NO ₃ ) ₂ ·3H ₂ O to the yellow solution, and continue stirring for 1 h to make the solution evenly mixed;

(7) The mixed solution was added to a 50 mL polytetrafluoroethylene autoclave, and transferred to an oven for heating for redox reaction at a reaction temperature of 190 °C and a reaction time of 5 h;

(8) After the reaction was completed, it was naturally cooled to room temperature, and the supernatant was poured out. The precipitate B was collected by centrifugation, and washed 4 times with deionized water and 3 times with absolute ethanol, until the supernatant appeared. clear and transparent;

(9) The obtained precipitate B was dried in a constant temperature vacuum drying oven at 60 °C for 10 h to obtain a CuO/WO ₃ hollow sphere composite material sensitive to H ₂ S gas;

(10) Mix 0.03 g of synthetic material with deionized water to form a slurry, then dip the slurry with a brush and evenly coat the surface of the cleaned ceramic tube. After air-drying at room temperature for 30 minutes, it was inserted into a Nichrome heater for aging (3 days) to enhance its stability. Put the prepared gas sensor into the gas chamber for gas sensor performance test.

Example 3

(1) Add 0.4 g of WCl ₆ to 35 mL of glacial acetic acid, stir with a magnetic stirrer for 30 min, and the solution changes from dark brown to blue;

(2) Pour the mixed solution into a 50 mL autoclave lined with polytetrafluoroethylene, and put it into an oven for hydrothermal reaction, the reaction temperature is 180 °C, and the reaction time is 12 h;

(3) After the reaction was completed, it was naturally cooled to room temperature, and the supernatant was poured out. The precipitate A was collected by centrifugation, and washed 4 times with deionized water and 4 times with anhydrous ethanol, until the supernatant was centrifuged. clear and transparent;

(4) The obtained precipitate A was dried in a constant temperature vacuum drying oven at 70 °C for 12 h, and then calcined in a muffle furnace. With air as the background gas, the temperature was raised to 500 °C at a heating rate of 2 °C/min. , the calcination time is 1 h, and the WO ₃ hollow sphere powder sensitive to H ₂ S gas is obtained;

(5) Weigh 0.2 g of WO ₃ obtained in step (4) into 30 mL of a mixed solution of deionized water and absolute ethanol (volume ratio is 1:1), and stir with a magnetic stirrer for 30 min to obtain a yellow solution ;

(6) Then add 0.035 g Cu(NO ₃ ) ₂ ·3H ₂ O to the yellow solution, and continue stirring for 1 h to make the solution evenly mixed;

(7) The mixed solution was added to a 50 mL polytetrafluoroethylene autoclave, and transferred to an oven for heating for redox reaction at a reaction temperature of 180 °C and a reaction time of 5 h;

(8) After the reaction was completed, it was naturally cooled to room temperature, the supernatant was poured out, the precipitate B was collected by centrifugation, and washed with deionized water for 4 times and anhydrous ethanol for 4 times, until the supernatant appeared. clear and transparent;

(9) The obtained precipitate B was dried in a constant temperature vacuum drying oven at 70 °C for 12 h to obtain a CuO/WO ₃ hollow sphere composite material sensitive to H ₂ S gas;

(10) Mix 0.03 g of synthetic material with deionized water to form a slurry, then dip the slurry with a brush and evenly coat the surface of the cleaned ceramic tube. After air-drying at room temperature for 30 minutes, it was inserted into a Nichrome heater for aging (3 days) to enhance its stability. Put the prepared gas sensor into the gas chamber for gas sensor performance test.

Claims (4)

1. a CuO/WO for H2S detection The preparation method of composite material is characterized in that: its step is: (1) Weigh 0.15-0.25 g of WO ₃ hollow sphere powder into a mixed solution of deionized water and absolute ethanol, stir evenly with a magnetic stirrer, and obtain a yellow solution; the volume ratio of deionized water and absolute ethanol is 1:1, magnetic stirring for 25-35min; (2) Then add 0.03-0.04 g Cu(NO ₃ ) ₂ ·3H ₂ O to the yellow solution, continue stirring to make the solution evenly mixed; the stirring time is 50-70 min, and the molar ratio of W to Cu is 6:1 ; (3) The mixed solution was added to a 50 mL polytetrafluoroethylene autoclave, and transferred to an oven for heating for hydrothermal reaction; the oven temperature was set to 170-190 °C, and the reaction time was 4-6 h; (4) After the reaction was completed, it was naturally cooled to room temperature, and the supernatant was poured out to obtain a precipitate B, which was collected by centrifugation, and washed several times with deionized water and absolute ethanol, respectively, until the supernatant was clear and transparent. The centrifugal speed is 2000-4000r/min, centrifugal washing is performed 6-7 times, the first 3-4 times are washed with deionized water, and the last 3-4 times are washed with absolute ethanol; (5) Put the obtained precipitate B into a constant temperature vacuum drying oven to dry for 8-12 h to obtain a CuO/WO ₃ hollow sphere composite material sensitive to H ₂ S gas; the temperature of the constant temperature vacuum drying oven is generally set to 60- 70 ℃, the vacuum degree is kept at 700-800Pa, the heating rate of muffle furnace calcination is 2 ℃/min, and the calcination time is 50-70 min at 490-510 ℃. 2. The preparation method of the CuO/WO3 composite material for H2S detection according to claim 1, characterized in that: the structural form of the _CuO /WO3 hollow sphere composite material is: the _CuO /WO3 hollow sphere form is CuO composite The morphology and structure of WO ₃ , the diameter of the hollow sphere is 1.2-1.4 μm, the CuO formed by the copper source is supported on the surface of the WO ₃ sphere, and the surface is rough, loose and porous. 3. The preparation method of CuO/WO3 composite material for H2S detection according to claim 1, characterized in that: the preparation method of _CuO /WO3 gas sensor gas sensor material: coating the _CuO /WO3 hollow sphere material On the surface of the ceramic tube, make a gas sensor element, which consists of a ceramic tube, platinum wire, gold electrode, heating wire and a sensitive layer; first take a small amount of synthetic material and mix it with deionized water to form a slurry, and then use a brush Dip the slurry and evenly coat it on the surface of the cleaned ceramic tube. After air-drying at room temperature for 30 minutes, insert it into a nickel-chromium alloy heater for aging for 3 days to enhance its stability. The gas sensing performance test is carried out in the gas inlet chamber. 4. The preparation method of CuO/WO3 composite material for H2S detection according to claim 1 or 3, characterized in that: the _CuO /WO3 gas sensor prepared with _CuO /WO3 hollow sphere composite material as the main material detects Improved H ₂ S gas response performance, continuous cycle detection of 0.1 to 50 ppm H ₂ S gas.

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